1. Field of the Invention
The present invention is directed to sensors, and, more particularly, to chemical sensors useful in monitoring environmental pollutants.
2. Description of Related Art
European patent application 381612 entitled "Construction of a medical probe with bonded light sensitive compound and use thereof", published 8 Aug. 1990, describes the bonding onto porous glass of an oxygen sensitive molecule and then the coating of the glass with a silicone resin. The probe is used to measure oxygen concentration. The patent states it might also be used for the measurement of pH. However, work completed during the course of making the present invention showed that a coating such as disclosed in that reference (a silicone) was not sufficiently permeable to water and ions for this pH sensitivity application. Silicones do have high permeability to oxygen but not to water or hydrogen ions.
Glass bound pH indicators are described in a reference by Harper Bruce, "Reusable glass-bound pH indicators", Analytical Chemistry, Vol. 47(2), 348-351 (1975). However, there is no disclosure or suggestion that these indicators may be used in a fiber optic device.
Polymeric acid-base indicators are described in a publication by M. Tahan et al, "Synthesis of some polymeric dyes", Isr J Chem , 1971, 9 (2), 191-200. These are not described for optical coatings.
A review of fiber optic chemical and biochemical sensors for environmental monitoring is described by A. L. Harmer, "Fibre Optic Chemical and Biochemical Sensors for Environmental Monitoring" in Optoelectronics for Environmental Science, S. Martellucci and A. N. Chester, Eds., Plenum Press (New York), pp. 39-43 (1989).
No prior art in the packaging of devices for rugged applications such as the one described herein is known. Thus, there remains a need for a chemically sensitive sensor for environmental monitoring.